1. Field of the Invention
This invention relates to blenders and more particularly to method and apparatus for thoroughly blending particulate or granular materials with virtually no recirculation required.
2. Description of the Prior Art
As storage bins or hoppers are filled with granular or particulate material, it often happens that an inhomogeneous distribution of material occurs. There may be several reasons for this result. In the first place, as material flows into a hopper, the material beneath the inlet nozzle piles up at the angle of repose of the material. In this case the larger particles often roll down the peak toward the sides of the hopper, leaving the finer particles in the central region. Inhomogeneity can also occur when the hopper is filled with different batches of the same material because of variations of composition of individual batches. When material is drawn off through an outlet at the bottom of the hopper, the material flows from the region directly above the nozzle. Thus the material will not be representative of the average characteristics of the material in the hopper.
Prior art attempts at a solution to this segregation problem typically included placing perforated blending tubes vertically within the hopper. Such tubes have openings spaced apart along their axes which allow material from all levels within the hopper to enter the tubes. The lower portion of the blending tubes communicate with the outlet nozzle so that a more nearly homogeneous mixture of the material issues from the outlet of the hopper.
In spite of many efforts to completely blend the particulate material, it is usually necessary in prior art blenders to specially treat at least the final portion of the discharge to achieve acceptable results. For example, U.S. Pat. No. 4,923,304, discloses that the first and last few pounds are not used, but instead are withdrawn and later remixed with fresh ingredients, ad re-poured, with these fresh ingredients, back into the dispensing apparatus.